The present invention relates to the field of networking in general and in particular to the field of wireless mesh networks where a spatially dispersed wireless node is admitted to the mesh network using an automatic join process method that incorporates time, frequency and space scheduling and synchronization of the inviting mesh network nodes.
Wireless networks are commonly designed by incorporating multiple Point to Point (PP) radio links connecting to each other, thus using fixed radio link connections to network the desired locations. Another commonly used network architecture employs a cell network topology such as Point to Multi Point (PMP) topology or a cellular based topology. Each node in such a network includes a radio and associated antenna. In the PMP topology, the network is controlled from a centralized location, such as a base station.
In a network including multiple independent point to point links, the addition of a new network node to the network is done manually by adding a new point to point wireless link. This is referred to as an admittance or admission process, in which the new network node is added to the network and initiates reliable radio communication with other components in the network. In a conventional admittance process, the radio link antennas are manually or mechanically aligned towards each other, until high quality reception is achieved. In the case of a PMP network, a base station is generally located near the center of the network and a new subscriber radio joins the network by communicating with the base station or multiple known base stations.
Two generic cases for admitting a new node to a network exist. In the first case, the subscriber has an omni-directional antenna. An example is a handset in a mobile communication system. In this case, the subscriber receives an invitation on a specific control channel and is invited by a base station covering his cell location. In the second case, the subscriber radio incorporates a directional antenna. Examples include satellite TV broadcast networks or PMP wireless access networks. A mechanical alignment process is done at the subscriber side alone whereby the subscriber antenna is aligned towards the base station to achieve optimum radio frequency (RF) signal reception. In the above-described previous networks, a new network node joins the network using mechanical alignment to achieve optimum reception.
The point to multi point alignment process is described in FIG. 1. FIG. 1 illustrates a portion of a prior art point to multi point wireless network 10. The network 10 includes a base station 11 and transceiver nodes 12, 19. The base station 11 has one or more antennas and associated transceivers for communicating in four 90 degrees sectors 13, 14, 15, 16 respectively, defined by axes 17a and 17b. The sectors 13, 14, 15, 16 are fixed in relation to the base station 11. The transceivers are assigned fixed frequencies for communicating in their associated sectors.
Each transceiver node 12, 19 corresponds to a subscriber radio. Transceiver node 12 includes an antenna having a single lobe or beam 18. The beam 18 is aligned mechanically by steering the antenna at the transceiver node 12 horizontally and vertically towards the location of the base station 11 until the beam 18 of the transceiver node 12 receives maximum signal strength from the transceiver associated with sector 13. The base station transceiver associated with sector 13 transmits data and invitation signals at its fixed frequency. Transceiver node 12 receives that frequency via its lobe or beam 18 and a signal strength indicator identifies the direction maximum received signal strength. This enables a human installer or motorized antenna driver to adjust the angular position of the antenna for maximum reception.
Alignment of transceiver node 19 is described in FIG. 1 as well. By rotating the transceiver antenna towards the base station 11, correct alignment is achieved with the base station transceiver and antenna associated with sector 14. Again, alignment is mechanical, by manually orienting the antenna beam or lobe to optimize signal reception.
In the example of point to multi-point communication, alignment is done at the remote subscriber unit, without changing the base station beam position, and the process is done by mechanical alignment. Although robust, the admittance process depends on costly manpower activity. In the event of network topology changes, a repeat operation is necessary to realign the subscriber radios or transceiver nodes towards the new base station location and to change the frequency to a newly assigned sector frequency.
Accordingly, there is a need for an improved method for admitting a new node to a network in general. In particular in a wireless mesh topology network where the network grows organically, a new node added to the network must join via one out of many already existing network nodes. An automatic process, which aligns electronically the directions of the reception beam of a joining node with the transmission beam of one of the inviting network nodes at specific time and frequency, is an important improvement to the mechanical alignment art.